The invention relates to a process for operating an internal combustion engine, in particular for operating an internal combustion engine for a motor vehicle equipped with a charging device such as a turbocharger.
The charge control in an internal combustion engine with a variable valve drive mechanism is essentially determined by, on the one hand, the intake valve stroke and/or the intake control time during which an intake valve frees the intake opening to the combustion space and thus the available air mass or charge can be supplied to the combustion space (or the charge is sucked in) and, on the other hand, due to the density of the available charge. The density, and thus the compression of the available charge, in an internal combustion engine with a charging device is in turn dependent on the type of charging device as such as well as on the type of operation and the particular operating point of the charging device used. In an exhaust gas turbocharger schematically indicated in FIG. 1 the pressure built up by the exhaust gas turbocharger is dependent on the position of the valve of a bypass, which is present in given cases, and the state prevailing in the exhaust tract (pressure, temperature, exhaust gas speed, . . . ). An increase of the charge amount for the combustion space can be accomplished, in one way, by lengthening the intake valve open time and, in another way, by increasing the charge pressure in the suction tract.
For operating an internal combustion engine with variable control of the gas exchange valves (in the following called valves), various processes are already known. In the MTZ Motortechnische Zeitschrift [JMT, Journal of Motor Technology] No. 62, pages 44-55, Der elektromagnetische Ventiltrieb—Systembaustein für zukünftige Antriebskonzepte [The Electromagnetic Valve Drive Mechanism—The System Building Block for the Drive Mechanism Concepts of the Future], Part 2, from the year 2001, describes, among other things, charge control of an internal combustion engine with a variable valve drive mechanism with the aid of the early intake closure control process and the late intake closure control process.
The early intake closure charge control process, or the late intake closure charge control process, is understood in the sense of the invention to mean a charge control process for an internal combustion engine, with a variable valve drive mechanism and without a charging device or without operation of the charger, in which the charge amount to be developed in each case based on a charge requirement is regulated via the open time or the control times of the intake valves.
In the early intake closure charge control process the driving is done in such a manner that the intake valves each remain open only up to the precise moment the desired charge amount is reached (intake valves open for a minimum time). In the late intake closure charge control process the driving of the intake valves is done in such a manner that they are open beyond the time required for the desired charge amount and the charge amount sucked in thereby, which is too much in comparison to the desired minimum charge amount, is expelled once again before the closing of the intake valve.
An extension of this charge control process is known through the so-called Miller process applied in many cases in internal combustion engines with a variable valve drive mechanism and a charging device, where in this Miller process, in the sense of the invention, the control of the desired charge amount is accomplished by driving the variably controllable intake valves according to the early intake closure charge control process or late intake closure charge control process in connection with the active operation of a charger.
In conventional naturally aspirating engines with a variable valve drive mechanism the pre-controlled charge corresponds, due to the cycle consistency at any time, therefore also in non-steady-state operation of the motor, to the motor charge actually present. It is problematic that in a supercharged motor with a variable valve drive mechanism it cannot be ensured that the pre-controlled charge also corresponds to the charge actually present in the next cycle since the charge pressure which is required to reach the desired charge cannot be presented in the following operational cycle. Thus, in non-steady-state operation there is always a difference between the charge pressure which is required and the charge pressure which is actually present. The change in the charge desired by the driver or a regulation system cannot be presented immediately due to the time delay of the build-up of charge pressure (a so-called turbolag).
The invention is based on the concept of charge control according to the above-described Miller process (early/late intake closure in connection with the operation of a charger). It is intended to specify a process by means of which one improves the non-steady-state response behavior of a supercharged internal combustion engine with a variable valve drive mechanism at least on the intake side. In particular, shorter times for meeting charge requirements which occur is intended to be ensured.
According to the invention this objective is realized as follows. Due to the fact that in an internal combustion engine during the operation of the charger a reserve (control time reserve or stroke reserve) available with respect to the intake closure control time and/or the stroke of a variable intake valve drive mechanism which is present is utilized in addition by in each operating cycle of the internal combustion engine an increased charge amount (in particular air mass) being supplied to the combustion space until the predefined theoretical charge is reached, the time required to meet the charge requirement can be reduced significantly and thus the response time of the internal combustion engine can be shortened.
Preferably, in the process according to the invention, the charger device is operated in such a manner that it is always provides the maximum possible charge pressure. For example, a controllable bypass device, as is present as a rule in an exhaust gas turbocharger, could thus be omitted. It is only important to the invention that at least, starting from a charge pressure increased in comparison to the present ambient pressure, a charge pressure increased still further is produced.
The intake valve drive mechanism in steady-state operation (without a sudden variation in the charge) is preferably driven in such a manner that (with respect to valve stroke and/or intake closure control time) at the maximum possible charge pressure the minimum charge amount required to meet the charge requirement is always precisely provided (early/late intake closure control process and/or intake valve stroke control). Due to this, during steady-state operation below the full charge (maximum developable motor charge, predefined by the motor control based on specific motor data) the described callable reserve with respect to valve stroke and/or intake closure control time (difference of the control time with minimum charge amount and the control time at UT or in the area of UT) is available.
If, after an, in particular sudden, charge requirement and a reserve call based on the charge requirement (for example, by lengthening the intake valve open time), perhaps due to a desire of the driver, the predefined target charge is reached, the at least one variable intake valve drive mechanism is preferably driven in such a manner that a certain reserve, in particular the intake closure control time reserve and/or stroke reserve originally present are/is restored.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.